The present invention relates to the general field of nozzles fitted to turbomachines. More particularly, it seeks to reduce aerodynamic noise from the jet generated at the outlet of the nozzles of airplane turbomachines that deliver separate flows, and to do so in particular while such an aircraft is taking off.
The nozzles fitted to airplane turbomachines generally comprise a centerbody surrounded by an inner barrel so as to form between them a first annular channel for a primary flow. An outer barrel surrounds the inner barrel so as to form a secondary annular channel for a secondary flow. The primary and secondary flows terminate, prior to being exhausted, in a converging portion, a throat, and a diverging portion. Overall these nozzle components are generally axially symmetrical in shape. The present invention relates more particularly to nozzles in which the centerbody is of the external type, i.e. having a trailing edge which is located downstream from the inner barrel.
The present invention seeks to reduce the jet noise generated at the outlet from such nozzles, in particular while an airplane is taking off, during which time the ejection speed of the primary and secondary flows is highly subsonic, i.e. about Mach 0.9 (high subsonic regime). At such flow speeds, two conditions must be satisfied: firstly it is necessary to conserve constant flow sections in three dimensions both in the neck and in the diverging portion of the nozzle in order to maintain the aerodynamic performance of the nozzle and guarantee flow rate conservation, and secondly it is necessary to maintain constant cross-sections over the entire circumference of the nozzle in order to avoid local zones of excess speed. This second requirement implies that the equivalent axially symmetrical section (as measured at the throat) must remain constant around the entire circumference of the nozzle, in all azimuth section planes. In a high subsonic regime, any local excess speed can lead to loss of aerodynamic performance, or to additional parasitic noise if a shockwave is produced.
In order to reduce the noise of the aerodynamic jet generated at the outlet from a nozzle, it is known to encourage mixing between the primary and secondary flows exiting the turbomachine. For this purpose, U.S. Pat. No. 5,924,632 proposes integrating lobes on the inner and outer barrels, with the free end of the centerbody presenting various possible shapes. Similarly, French patent No. 2 529 956 describes a system for ejecting mixed flows in which the inner barrel is provided with lobes and the centerbody is provided in part with undulations. Applying those technologies to a flow at a high subsonic rate is unsatisfactory. The above-described requirements are not satisfied, and in particular the requirement relating to conserving constant cross-sections around the entire circumference of the nozzle. This leads to local excess speeds which, in the high subsonic regime, generate shock waves which generate additional parasitic noise and which also reduce the aerodynamic performance of the nozzle.